The study is designed to define the physiological mechanisms of control of ovum transport in the rabbit and the sites at which progesterone and estrogen act to accelerate and delay transport. The interrelationships between timing of administration of hormones, effects on isthmic resistance and oviductal contractility, and ovum transport rates will be assessed. Inference will be made concerning the relative contribution of ciliary, secretory and muscular activity on transport and delay of ova. Donor ova or ovum surrogates of different sizes and densities will be transferred to oviducts at various time intervals after ovulation and location of ova determined by clearing and flushing techniques. Ovum transport rates will be correlated with isthmic resistance and oviductal contractility.